This doubt creates speculation, and the more doubt, the greater the speculation. You end up in the strangeness of the prime minister granting radio interviews to respond to responses to a speech he hasn’t given.

This is politics eating itself. Why is it happening?

There are usually two sorts of big speeches for political leaders. There are the speeches where they really have to say something, and those where they really have something to say. Into the first category fall unavoidable events like party conference or the Mansion House speech. President Obama can’t turn up to the State of the Union and say “The state of the union is much the same as last year”. Whether they want to speak or not, a top-flight politician has to turn up and has to have something interesting to say.

These set pieces loom over the rhythms of politics and the lives of speechwriters alike. Policies are called for, scrutinised. Jokes are tested out. Friends and allies are consulted, with varying levels of usefulness. One No 10 speechwriter even used to refuse to go on holiday over the summer, just in case inspiration for the conference speech struck her boss while walking on the beach and a redraft was needed, pronto.

The advantage of all this stress is that the long search for a theme tends to create its own momentum. The speech can be bad or brilliant, but you can usually tell what it’s about.

The second type of speech is more direct. They tend to happen when a minister thinks there’s something that needs to be said, and needs to be said now. One of the greatest examples of this was Lyndon Johnson’s speech to Congress in March 1965, responding to the riots in Selma, Alabama, when he “summoned into convocation” the US Congress to argue there must be no more delay in implementing voting rights and civil rights.

These speeches usually have an urgency, a vigour and a passion because they make an argument that the politician believes must be made and must be made immediately. They crackle off the page, even when read half a century later.

Yet David Cameron’s team may have created a remarkable third category, a speech where they don’t need to announce anything, don’t really have anything much to announce, and don’t really want to announce it. No wonder then, that the process of making the speech has been tortured.

Today, we ended up with the farcical situation where No 10 announced that the prime minister’s speech will now happen this Friday, making it the first scheduled speech I’ve ever known that has both been postponed because it wasn’t urgent and brought forward to address a crisis.

So why is Cameron making a speech at all? We already know that David Cameron wants to repatriate powers from the EU. He doesn’t need a speech to tell us that. He just needs to do it. We already know that David Cameron wants to stay in the European Union but thinks it needs to change. He doesn’t need a speech to tell us that, he just needs to secure the changes he wants.

The best explanation is that this speech is essentially a plea for time and space. The Tory Eurosceptics want powers repatriated or a referendum on an exit immediately. Our European partners don’t want either.

So the prime minister needs to persuade his own party to give him time to win some concessions, and needs to persuade his partners to give him those concessions.

Ideally, he wouldn’t be giving such a speech at all, but after two and a half years of lively rhetoric but practical inaction on these same issues, his party are impatient and his partners are irritated. So he has to come up with a list to persuade one audience he’s acting, and at the same time convince another audience that he’s being forced to act. The speech isn’t really about setting out a policy or achieving an aim. It has by virtue of the government’s policy confusion, itself become the policy.

This speech is about saying “Of course David Cameron wants action on Europe. He must do. He’s making a big speech about it.” Which is why it’s very likely to be a letdown.